1. Field of the Invention
The present invention relates to a method of processing images by expanding, contracting, rotating, or the like, and also to an apparatus for the same.
2. Description of the Related Art
A typical procedure applied for recording a desired image includes the steps of: inputting an original image with an input device such as an input scanner; expanding, contracting, or rotating the original image with an image processing apparatus; and outputting the processed image with an output device such as a printer.
When an image of 1,000 pixels in length by 1,000 pixels in width captured by an input device is to be output as an image of 100 mm in length by 100 mm in width with an output device having an output resolution of 20 pixels per mm, it is required to expand the image of 1,000 .times.1,000 pixels to an image of 2,000.times.2,000 pixels with an image processing apparatus. Pixel-by-pixel interpolation is a conventional technique applied for such expansion of images.
Typical methods of pixel interpolation include a nearest neighbor method for interpolating from a nearest pixel to a target point of interpolation, and a linear interpolation method for linearly interpolating from four pixels near to a target point of interpolation.
The conventional method of pixel-by-pixel image processing, like expansion, contraction, or rotation of an original image may lower the resolution of a resulting image than that of the original image.
In expansion of images by pixel interpolation, for example, not only the resolution of an original image but the resolution of an expanded image depends upon the resolution of an input device. The pixel interpolation may accordingly cause a blur in the resulting image (especially, in linear interpolation method) or cause jaggy portions in curved or inclined straight lines of the obtained image (especially, in nearest neighbor method), thereby deteriorating the image.